1. Field of the Invention
The present invention pertains generally to cooling apparatus, and more particularly, but not by way of limitation, to a cooling apparatus using xe2x80x9clow profile extrusions.xe2x80x9d More specifically, the cooling apparatus of the present invention is particularly suited to cooling high watt density subassemblies such as power amplifiers and filters commonly used in modern telecommunications equipment.
2. History of the Related Art
As explained in greater detail below, the cooling system of the present invention is capable of removing heat generated by electronic equipment in a particularly dense environment, as is commonly encountered in a cabinet housing power amplifiers for telecommunications equipment. In these types of applications, space is extremely limited within the cabinet, and control of thermal cycling is critical.
As used in this document, the term xe2x80x9clow profile extrusionxe2x80x9d refers to an integral or unitary piece of metal having a series of micro extruded hollow tubes or channels formed therein for containing a fluid. The micro tubes or channels will typically have an effective diameter ranging from about 0.0625 inches to about 0.5000 inches, but can also have significantly smaller diameters.
Preferred low profile extrusions are sold by Thermalex, Inc. of Montgomery, Ala. A brochure entitled xe2x80x9cThermalex, Inc.xe2x80x94Setting A Higher Standard in Aluminum Extrusionsxe2x80x9d (herein after the xe2x80x9cThermalex Brochurexe2x80x9d) provides additional detail regarding the Thermalex low profile extrusions and is incorporated herein by reference. U.S. Pat. No. 5,342,189, which is incorporated herein by reference, provides additional detail regarding an extrusion die for making such low profile extrusions. U.S. Pat. No. 5,353,639, which is incorporated herein by reference, provides additional detail regarding a method and apparatus for sizing a plurality of micro extruded tubes used in such low profile extrusions. These low profile extrusions are commercially available in strip form (having a generally rectangular geometry) or coil form (a continuous strip which is coiled for efficient transport).
It is notable, that although the micro tubes or channels described herein have an effective diameter, because the low-profile extrusion is formed of a single piece of metal which is extruded, it is possible to form channels with square, rectangular, or almost any geometry. Moreover, it is possible to extrude fins, grooves or wick structures on the interior of the channels without any additional machining steps. The low profile extrusions preferably have multi-void micro extruded tubes designed to operate under the pressures and temperatures required by modern environmentally safe refrigeration fluids and to resist corrosion. Such low profile extrusions are preferably formed from aluminum, although it is possible to use other metals or alloys which are sufficiently malleable to be extruded and have relatively high heat conductivity.
The present invention discloses a low profile cooling system which is particularly well suited for cooling power amplifiers and other electronic components housed within a wireless telecommunications base station. Telecommunications base stations are typically cabinet-like structures, containing racks of electronic equipment, which are located outdoors and exposed to a variety of environmental conditions including temperature variations, rain and other natural conditions. These base stations further include a large number of power amplifiers and other electronic components mounted on cards or metal plates for the conduction of heat. The metal plates, which act as heat sinks, will typically have power amplifiers and other components mounted on one side and fins or other cooling structures mounted on the opposite site. Typically, ambient air will be circulated in high volumes throughout the entire cabinet and across the fins of each metal plate to result in the removal of heat from the electronic components by conduction into the plate and convection from the plate to the air.
In one embodiment of the present invention, a closed liquid loop cooling system provides superior heat removal to the conventional air circulation method. The low profile extrusions are fitted with end caps or manifolds at opposite ends, and conduits or plumbing to carry a heat transfer fluid to and from each of the extrusions. The cooling system of the present invention generally comprises one or more low profile extrusions, a heat transfer fluid, a means for circulating the heat transfer fluid, and means for removing heat from the heat transfer fluid.
As noted earlier, each low profile extrusion has a plurality of micro tubes with micro tube inlets and micro tube outlets, and a substantially flat exterior surface adapted for receiving heat from at least one heat generating component. The end caps interconnect the micro tube inlets and outlets of each low profile extrusion in fluid communication and further connect the low profile extrusions in fluid communication with each other in either a series or parallel configuration. One or both of the end caps or manifolds may also contain openings or connections for a fluid input tube and a fluid output tube. The means for circulating the heat transfer fluid circulates the fluid through the inlet tube, the end cap inlet, the plurality of micro tubes in each low profile extrusion, the end cap outlet, and the outlet tube.
In one embodiment, heat generated by the electronic components, such as power amplifiers, is conducted away from the components through the metal plate on which they are mounted, into the low profile extrusions, and then passed to the heat transfer fluid circulating therein. The heat transfer fluid is pumped by the circulating means into and out of each low profile extrusion and through the means for removing heat from the fluid before being recirculated and passed again through the low profile extrusions.